This is a study of passive intermembrane protein transfer of intrinsic proteins. The physical parameters governing this process have been identified in the transfer of erythrocyte proteins to model membranes. The proposed research will examine transfer of proteins from model membranes to cells, with the aim of developing passive transfer as a noninvasive means of modifying the transport and antigenic properties of biological membranes. The possibility of cell-to-cell transfer by this mechanism will be explored, employing immunological recognition as a way to detect very low levels of transfer. Mechanisms whereby cells control such protein exchange in vivo will be studied, with particular attention to the roles of cell cytoskeletons and membrane phospholipid distributions. Protein transfer from cells to model membranes will be used to probe the association between cell surface proteins and membrane cytoskeletons. The overall objective is to evaluate passive protein transfer as a mechanism for modification of membrane properties, either in natural processes or as a research instrument.